-Tank that is at least 2.5 gallons
-Water conditioner (SeaChem Prime or Stress Coat+ are good products for this)
-Adjustible, Submersible Heater (25W-50W is best)
-Silk Plants, NO PLASTIC
-Cave or decoration for hiding (No sharp edges!)
-Food made for Bettas (Pellets and/or flakes, dried/frozen bloodworms, etc, there's a lot out there...)
Recommended:
-A very gentle filter
-Aquarium Salt
-Epsom Salt
-Medicine to have on hand.
I hope I didn't forget anything.